I'm reopening the thread... I thought that I had found the problem but it seems to be something else. First of all, I discovered that the leaking happened during a period that the car was parked outside for two weeks. Hence, the water has to come from rain/from above. Also, this time, the puddle was much larger...
I took the plastic parts off and saw that the the rubber, round seal of the door had water in it. That water must come from the door! I guess that some water from the window leaks inside the door (normal). That water should leave the door again through the little holes in the bottom of the door. Since I park my car outside and on an incline, the drains my not work properly and the water starts to leak through the hole in the seal (see pic w/ my finger). The hole in the seal makes contact with the fabric on the threshold of the door. That sucks up the water and generally spreads it under the floor mat. (see pic w/ wet spot).
Can you guys still follow this?!?
I was wondering how to solve the problem. First of all, am I right? Is this the real cause of the problem? Should I replace the seal? All seals should have holes so how does this solve the problem? Park the other way around on the slope (difficult...) ?!? Any experiences, dealer advise?